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Wireless# Guide to Wireless Communications

Wireless# Guide to Wireless Communications. Chapter 9 Wireless Metropolitan Area Networks. Objectives. Explain why wireless metropolitan area networks (WMANs) are needed Describe the components and modes of operation of a WMAN

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Wireless# Guide to Wireless Communications

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  1. Wireless# Guide to Wireless Communications Chapter 9 Wireless Metropolitan Area Networks

  2. Objectives • Explain why wireless metropolitan area networks (WMANs) are needed • Describe the components and modes of operation of a WMAN • List the range of WMAN technologies, including FSO, LMDS, MMDS, and 802.16 (WiMAX) • Explain how WMANs function • Outline the security features of WMANs Wireless# Guide to Wireless Communications

  3. What is a WMAN? • Wireless metropolitan area networks (WMANs) • Provide wireless connectivity across a substantial geographical area such as a large city • WMANs primary goals • Extend wired networks beyond a single location • Without the expense of high-speed cable-based connections • Extend user mobility throughout a metropolitan area • Provide high-speed connections to areas not serviced by any other method of connectivity Wireless# Guide to Wireless Communications

  4. Last Mile Wired Connections • Last mile connection • Link between a customer and ISP • Most last mile connections use copper wiring • Copper-based digital communications lines (T1) • Require the signal to be regenerated every 6,000 feet (1.8 KM) • Last mile delivery of telephone and data lines has long been a problem for the carrier • Must be able to justify the cost of installing wired connections to remote areas Wireless# Guide to Wireless Communications

  5. Last Mile Wired Connections (continued) Wireless# Guide to Wireless Communications

  6. Last Mile Wired Connections (continued) Wireless# Guide to Wireless Communications

  7. Last Mile Wireless Connections • Microwaves are higher frequency RF waves • In the 3 to 30 GHz range of the electromagnetic spectrum known as super high frequency (SHF)band • Microwave towers are installed roughly 35 miles (56 kilometers) apart from each other • A microwave link operating at 4.0 GHz carries 1800 voice calls simultaneously • Fixed wireless • Wireless as the last mile connection for buildings • Backhaul connection • Company’s internal infrastructure connection Wireless# Guide to Wireless Communications

  8. Baseband vs. Broadband • Broadband transmission • Sends multiple signals at different frequencies • Baseband transmission • Treats the entire transmission medium as if it were only one channel • Only one signal can be sent at a time Wireless# Guide to Wireless Communications

  9. Baseband vs. Broadband (continued) Wireless# Guide to Wireless Communications

  10. Land-Based Fixed Broadband Wireless • Technologies • Free Space Optics (FSO): IR-Based • Local multipoint distribution service (LMDS) • Multichannel multipoint distribution service (MMDS) • IEEE 802.16 (WiMAX) Wireless# Guide to Wireless Communications

  11. Fiber-Optic Cable • Thin strand of glass (core) • Light impulses • Source: Laser or Light Emitting Diode (LED) • Light travels at a speed of 186,000 miles/second • Immune to electromagnetic interference • Hard to intercept Wireless# Guide to Wireless Communications

  12. Free Space Optics • Free space optics (FSO) • Optical, wireless, point-to-point, line-of-sight broadband technology • Excellent alternative to high-speed fiber-optic cable • Can transmit up to 1.25 Gbps at a distance of 4 miles (6.4 kilometers) in full-duplex mode • Uses infrared (IR) transmission instead of RF • Transmissions are sent by low-powered invisible infrared beams through the open air • FSO is a line-of-sight technology • FSO uses the unlicensedspectrum above 300 GHz • Limited radiation power Wireless# Guide to Wireless Communications

  13. Free Space Optics (continued) Wireless# Guide to Wireless Communications

  14. Free Space Optics (continued) • Advantages of FSO • Cost (ex. $400,000 for fiber-optic vs. $60,000 for FSO) • Speed of installation: (days vs. months) • Transmission rate • Security: IR are much harder to intercept than RF • Disadvantages of FSO • Atmospheric conditions impact FSO transmissions • Scintillation • Temporal and spatial variations in light intensity caused by atmospheric turbulence (pockets of air with rapidly changing densities) Wireless# Guide to Wireless Communications

  15. Free Space Optics (continued) • Disadvantages of FSO (continued) • FSO overcomes scintillation by sending the data in parallel streams (spatial diversity solution) • From several separate laser transmitters (7.8” apart) • Dealing with fog • Increase the transmit power of the signal (light intensity) • Signal interference (ex. Flying birds) • Tall buildings or towers can move due to earthquake or winds affecting the aim of the beam. Solutions: • Beam Divergence: spread the beam forming an optical cone • Active Tracking: movable mirrors to control the direction of the beams are adjusted based on the feedback Wireless# Guide to Wireless Communications

  16. Free Space Optics (continued) Wireless# Guide to Wireless Communications

  17. Free Space Optics (continued) • FSO applications • Last mile connection: connect end users with ISPs or other networks • LAN connections: (ex. Buildings in a large campus) • Fiber-optic backup: (redundant link) • Backhaul: (ex. cellular telephone towers to wired facilities) Wireless# Guide to Wireless Communications

  18. Local Multipoint Distribution Service (LMDS) • Local multipoint distribution service (LMDS) • Fixed broadband technology that can provide a wide variety of wireless services: • High-speed Internet access • Real-time multimedia file transfer • Remote access to local area networks • Interactive video, video-on-demand, video conferencing • Telephone service • Can transmit from 51 to 155 Mbps downstream and 1.54 Mbps upstream • Low-powered RF waves • Over a distance of up to about 5 miles (8 kilometers) Wireless# Guide to Wireless Communications

  19. Local Multipoint Distribution ServiceCont. • Local: FCC grants licenses to carriers for a specific area • Base station: point-to-multipoint transmission • Remote Stations: point-to-point transmission • Distribution: various types of information (video, data, Internet, voice) • Services: depend on the carrier (video, data, Internet, voice) Wireless# Guide to Wireless Communications

  20. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  21. Local Multipoint Distribution Service (LMDS) (continued) • Frequency • Based on high frequency, low-powered signals over short distances • LMDS used the following ranges of frequencies • 27.5 GHz and 28.35 GHz (850 MHz) • 29.1 GHz and 29.25 GHz (150 MHz) • 31.075 GHz, and 31.225 GHz (150 MHz) Wireless# Guide to Wireless Communications

  22. Local Multipoint Distribution Service (LMDS) (continued) • Architecture • Cells (like a cellular telephone system) • LMDS is a fixed wireless technology for buildings • Factors that determine the cell size (2 to 5 miles) • Line-of-sight (tall buildings obstructing shorter ones) • Antenna height (antennas on high buildings broaden the coverage area) • Overlapping cells: allows for more coverage by the additional cells and transmitters • Rainfall: requires to reduce the cell size or increase transmission power Wireless# Guide to Wireless Communications

  23. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  24. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  25. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  26. Local Multipoint Distribution Service (LMDS) (continued) • Architecture (continued) • LMDS signals are broadcast from radio hubs that are deployed throughout the carrier’s market • Area in which the LMDS provider has a license to use a certain frequency • Hub connects to the service provider’s central office • Can connect to other networks, such as the Internet • Equipment at the receiving site • 12- to 15-inch diameter directional antenna • Digital radio modem • Network interface unit Wireless# Guide to Wireless Communications

  27. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  28. Local Multipoint Distribution Service (LMDS) (continued) Wireless# Guide to Wireless Communications

  29. Local Multipoint Distribution Service (LMDS) (continued) • Architecture (continued) • LMDS systems can use either: • Time division multiple access (TDMA) • Frequency division multiple access (FDMA) • Modulation techniques • Quadrature phase shift keying (QPSK) • Quadrature amplitude modulation (QAM) Wireless# Guide to Wireless Communications

  30. Local Multipoint Distribution Service (LMDS) (continued) • Advantages of LMDS • Cost: comparing to fiber-optic • service area: expandable by adding one cell at the time • data capacity: 1,300 MHz of spectrum in local areas supports 16,000 telephone calls and 200 video channels • Disadvantages of LMDS • LMDS requires a direct line of sight between buildings • LMDS signals are susceptible to interference from rain and fog Wireless# Guide to Wireless Communications

  31. Multichannel Multipoint Distribution Service (MMDS) • Multichannel multipoint distribution service (MMDS) • Fixed broadband wireless technology similar to LMDS • Can transmit video, voice, or data signals at 1.5 to 2 Mbps downstream and 320 Kbps upstream • At distances of up to 35 miles (56 kilometers) • MMDS is sometimes called wireless cable • Can broadcast 300 channels • Internet access using MMDS is an alternative to cable modems and DSL service • Uses 2.1 GHz and 2.5 through 2.7GHz band Wireless# Guide to Wireless Communications

  32. Multichannel Multipoint Distribution Service (MMDS) (continued) • Layout • MMDS hub is typically located on a high point • Uses a point-to-multipoint architecture that multiplexes communications to multiple users • Tower has a backhaul connection to carrier’s network • Carrier network connects with the Internet • MMDS signals can travel longer distances • Provide service to an entire area with only a few radio transmitters • MMDS cell size can have a radius of up to 35 miles (56 kilometers) Wireless# Guide to Wireless Communications

  33. Multichannel Multipoint Distribution Service (MMDS) (continued) • Layout (continued) • Pizza box antenna • 13 by 13 inches antenna used at receiving site • Aimed at the hub to receive the MMDS signal • Cable runs from the antenna to an MMDS wireless modem • Modem can connect to a single computer or an LAN Wireless# Guide to Wireless Communications

  34. Multichannel Multipoint Distribution Service (MMDS) (continued) Wireless# Guide to Wireless Communications

  35. Multichannel Multipoint Distribution Service (MMDS) (continued) Wireless# Guide to Wireless Communications

  36. Multichannel Multipoint Distribution Service (MMDS) (continued) • Advantages of MMDS • Signal strength: less susceptible to interference, more capability to penetrate buildings • Cell size: covers larger areas than LMDS • Cost: lower equipment cost because of lower frequency • Disadvantages of MMDS • Physical limitations: line of sight (buildings obstructions) • Frequency sharing: Large number of users in large area share same channels reducing the rate to 1.5 Mbps • Security: no encryption provided by MMDS, additional security measures are added by users • Availability of the technology: limited to some areas in the US Wireless# Guide to Wireless Communications

  37. IEEE 802.16 (WiMAX) • Standard for wireless broadband metropolitan area networks • 802.16 supports enhancements and extensions to the MAC protocols • Base station (BS) can communicate with another BS • And also directly with subscriber stations (SS) • WiMAX Forum • Promotes the implementation of 802.16 by testing and certifying equipment • WiMAX stands for worldwide interoperability for microwave access Wireless# Guide to Wireless Communications

  38. Shortcomings • Both of LMDS and MMDS don’t provide connectivity with mobile devices • FSO cannot support mobile communications because of it directional requirements • Neither of FSO, LMDS, or MMDS is based on an open standard: equipments must be purchased from the same manufacturer or provider Wireless# Guide to Wireless Communications

  39. IEEE 802.16 (WiMAX)Worldwide interoperability for Microwave Access • Introduced by IEEE in 2000 as a standard for WMAN • Standardizing fixed broadband wireless connections • Alternative to fiber-optic, cable modem, and DSL • Enhancements and extensions to the MAC protocols • Base stations can communicate with subscriber stations (mobile devices or stations attached to LAN) • Base stations can communicate with each other directly. • WiMAX Forum: test and certifies equipments for compatibility and interoperability Wireless# Guide to Wireless Communications

  40. IEEE 802.16 (WiMAX) • Range measured in miles • Data Rates • 70 Mbps in the 2 to 11 GHz bands • Up to 120 Mbps at short distances (large office environment) 10 to 66 GHz band • Installation • CPE are easy to install and require minimum or no configurations. • Mount the antenna in the direction if the BS. Wireless# Guide to Wireless Communications

  41. WiMAX Applications • Applications • Suitable for backhaul applications for business • Last mile delivery applications for Internet connectivity • Supports simultaneous voice, video, and data transmission • Suitable for voice-over-IP (VoIP) connections • Enables vendors to create customer premises equipment (CPE) • Can also be deployed as a point-to-point network • Provide broadband access to rural and remote areas Wireless# Guide to Wireless Communications

  42. WiMAX Applications (continued) • Applications (continued) • WiMAX CPE devices will support TV (video), telephone (voice), and data on the same network • WiMAX MAC layer makes it easy for carriers to deploy the network • Range of a WiMAX network is measured in miles • Cellular phone operators can easily incorporate WiMAX networks Wireless# Guide to Wireless Communications

  43. Standards Family Overview • 802.16-2001 and 802.16-2004 standards • Define the interface specification for fixed, point-to-multipoint broadband WMANs • 802.16a • Supports systems in the 2 GHz to 11 GHz band • 802.16c • Provided clarifications related to performance evaluation and testing • 802.16e • Defines specifications for a mobile version of WiMAX • 2 Mbps for slow moving devices, 320 kbps for fast-moving devices Wireless# Guide to Wireless Communications

  44. WiMAX Protocol Stack • PHY layer supports multiple frequency bands and several modulation techniques • WiMAX MAC layer is connection oriented • Includes service-specific convergence sublayers • That interface to the upper OSI layers • WiMAX offers multiple simultaneous services through the same link • Asynchronous transfer mode (ATM), IPv4, IPv6, Ethernet, and VLAN Wireless# Guide to Wireless Communications

  45. WiMAX Protocol Stack (continued) Wireless# Guide to Wireless Communications

  46. WiMAX Protocol Stack (continued) • PHY layer • Five variations of the PHY layer in 802.16 • First two are based on the modulation of a single carrier signal • Transmission is half-duplex • Each frame is subdivided into one uplink subframe and one downlink subframe • Subframes are further divided into a series of time slots • Burst is a data transmission to or from a single device • Use time division duplexing (TDD) Wireless# Guide to Wireless Communications

  47. WiMAX Protocol Stack (continued) Wireless# Guide to Wireless Communications

  48. WiMAX Protocol Stack (continued) • PHY layer (continued) • WiMAX allows two different frequency channels • Frequency division duplexing (FDD) • WiMAX can support half-duplex and full-duplex equipment • Variations of the PHY layer specified in the standard • WirelessMAN-SC (single carrier) • WirelessMAN-SCa (single-carrier access) • 802.16 standard also provides support for non-line-of-sight applications Wireless# Guide to Wireless Communications

  49. WiMAX Protocol Stack (continued) Wireless# Guide to Wireless Communications

  50. WiMAX Protocol Stack (continued) • PHY layer (continued) • Additional PHY layer transmission mechanisms to support NLOS applications • WirelessMAN-OFDM • Uses TDMA • WirelessMAN-OFDMA • Divides the available channel into a large number of orthogonal subcarriers • Third transmission mechanism • Wireless high-speed unlicensed metro area network (WirelessHUMAN) Wireless# Guide to Wireless Communications

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